<template>
  <div class="slider" ref="slider">
    <div class="slider-group" ref="sliderGroup">
      <slot></slot>
    </div>
    <div class="dots">
      <span v-if="dots" class="dot" v-for="(item, index) in dots" :class="{active: currentPageIndex === index}"></span>
    </div>
  </div>
</template>

<script>
import { addClass } from 'common/js/dom'
import BScroll from 'better-scroll'
export default {
  props: {
    loop: {
      type: Boolean,
      default: true
    },
    autoPlay: {
      type: Boolean,
      default: true
    },
    interval: {
      type: Number,
      default: 4000
    }
  },
  data() {
    return {
      dots: [],
      currentPageIndex: 0
    }
  },
  mounted() {
    // 浏览器17秒刷新一次
    setTimeout(() => {
      this._setSliderWidth()
      this._initDots()
      this._initSlider()
      if (this.autoPlay) {
        this._play()
      }
    }, 20)

    window.addEventListener('resize', () => {
      if (!this.slider) return
      // 窗口改变的大小时重新计算clienWidth 此时不需要再加上两个多余的width
      this._setSliderWidth(true)
      this.slider.refresh()
    })
  },
  destroyed() {
    clearTimeout(this.timer)
  },
  methods: {
    _setSliderWidth(isResize) {
      this.children = this.$refs.sliderGroup.children
      let width = 0
      let sliderWidth = this.$refs.slider.clientWidth
      for (let i = 0; i < this.children.length; i++) {
        let child = this.children[i]
        addClass(child, 'slider-item')
        child.style.width = sliderWidth + 'px'
        width += sliderWidth
      }
      if (this.loop && !isResize) {
        width += 2 * sliderWidth
      }
      this.$refs.sliderGroup.style.width = width + 'px'
    },
    _initDots() {
      this.dots = new Array(this.children.length)
    },
    _initSlider() {
      this.slider = new BScroll(this.$refs.slider, {
        scrollX: true,
        scrollY: false,
        momentum: false,
        snap: true,
        snapLoop: this.loop,
        snapThreshold: 0.3,
        snapSpeed: 400
      })

      this.slider.on('scrollEnd', () => {
        let pageIndex = this.slider.getCurrentPage().pageX
        if (this.loop) {
          pageIndex -= 1
        }
        this.currentPageIndex = pageIndex

        if (this.autoPlay) {
          this._play()
        }
      })

      this.slider.on('beforeScrollStart', () => {
        if (this.autoPlay) {
          clearTimeout(this.timer)
        }
      })
    },
    _play() {
      let pageIndex = this.currentPageIndex + 1
      if (this.loop) {
        pageIndex += 1
      }
      this.timer = setTimeout(() => {
        this.slider.goToPage(pageIndex, 0, 400)
      }, this.interval)
    }
  }
}
</script>

<style scoped lang='stylus'>
  @import '~common/stylus/variable'

  .slider
    min-height 1px
    .slider-group
      position relative
      overflow hidden
      white-space nowrap
      .slider-item
        float left
        box-sizing border-box
        overflow hidden
        text-align center
        a
          display block
          width 100%
          overflow hidden
          text-decoration none
        img
          display block
          width 100%
    .dots
      position absolute
      left 0
      right 0
      bottom 12px
      text-align center
      font-size 0
      .dot
        display inline-block
        margin 0 4px
        width 8px
        height 8px
        border-radius 50%
        background $color-text-l
        &.active
          width 20px
          border-radius 5px
          background $color-text-ll
</style>
